Light-sensitive element



March 2, 1943. w. c. TOLAND ETAL 2,312,852

LIGHT-SENSITIVE ELEMENT Filed Jan. 24, 1940 E29. 1 I V /'A Patented Mar.2, 1943 William Craig Toland and Ellis Bassist, Brookline, Mass.,assignors to William Craig Toland, Brookline, Mass., as trusteeApplication January 24, 1940, Serial No. 315,412

4 Claims.

This invention relates to light-sensitive elements and more especiallyto light-sensitive elements for use in connection with printing.

A chief object of the invention is to improve light-sensitive elementsand to devise a novel light-sensitive product in which alight-sensitizing salt, such as a silver compound or other similar metalcompound, is associated with a support suitable for comprising aplanographic printing plate. A further object is a simpler, cheaper, andmore eifective light-sensitive member. The invention also aims toindicate an improved method of preparing planographic printing platesand to present a plate having a novel combination of printing andnon-printing portions.

Attainment of these and other objects will be readily understood fromthe following description when read in connection with the accompanydrawing and the novel features will be more particularly pointed out inthe appended claims. R.

In the accompanying drawing:

Fig. 1 isa diagrammatic view illustrating a. planographic printing platesupport employed in forming the plate of the invention.

Fig. 2 is a diagrammatic view illustrating a coating step resorted to incarrying out the'invention.

Fig. 3 is still another diagrammatic view illustrating the step ofcoating a light-sensitive material on a plate construction similar tothat shown in Fig. 2; and

Fig. 4 is still another diagrammatic view illustrating the coatingindicated in Fig. 3 exposed and developed to comprise a printing plate.

In a co-pending application, Ser. No. 170,762, filed Oct. 25, 1937,means have been described and claimed for forming a planographicprinting plate. Water retention is effected by the use of hydrophilicsynthetic materials in the nonprinting portions of the plate and thehydrophilic materials may, if desired, be associated with supports ofnon-metallic character, such as those of paper or plastic materials. Oneexample of a hydrophilic material described in the above indicatedapplication, suitable for this purpose, is polyvinyl alcohol. Othervinyl compounds and other synthetic normally hydrophilic resins may beemployed.

In the accompanying drawing, numeral I denotes a planographic printingplate base more particularly shown in Figure 1. Various materials may beemployed to comprise the support I and a preferred material consists ina laminated paper and/or resin structure as described and claimed in ourPatent No. 2,280,985 issued April 28, 1942.

Upon the support I is applied a film of a hydrophilic material 2, suchas a vinyl compound, as described in the above referred to co-pendingapplication Ser. No. 170,762, and as is further illustrated in Fig. 2 ofthe drawing. It is pointed out that the coated member shown in Fig. 2comprises a workable planographic printing plate base presenting awater-receptive surface of ungrained and non-metallic character.

In accordance with the invention. a photosensitive emulsion is preparedand a coating 3 of the emulsion is applied directly over the hydrophiliclayer 2, as has been illustrated in Fig. 3. The emulsion contains ahighly light-sensitive agent which is adapted to maintaining itssensitivity for extended periods of time. As one example of a suitableemulsion, there may be cited a silver halide salt such as silverbromide, mixed with a colloid as a gelatin. The coating is allowed todry and thereafter protected from exposure to light to comprise alight-sensitive ele-. ment which may be kept in darkness for extendedperiods and at any desired time exposed and developed to comprise aplanographic printing plate.

There results a useful intermediate printing plate product which may bestored and shipped in an unexposed state, and which may be developed atany desired time with avoidance of the .many objections present inconnection with developing a printing plate sensitized with achromicsalt. It may be desired to employ other silver halides and othercolloids mixed with them.

In accordance with the method of the invention, the use of gelatin forcomprising the printing portions of a planographic plate is made,

practical by combining it with the metal salts noted and then effectinga bonded association with a planographic base in a manner not heretoforepractical.

In detail, the method of preparation of a planographic printing plateconsists in exposing with a photographic negative a light-sensitizedplate support such as that above described and illustrated in Fig. 3.Exposure of the silver salt provides a latent image which may bedeveloped in a developer such as hydroquinone, metal catechol and thelike. fixed in a non-hardening fixing bath of conventional nature, andthe resulting silver image in the gelatin is thereafter converted bytreatment with ammonium bichromate to silver chromate. The colloidcontaining the unexposed light-sen- The print can then be sitive saltsis finally washed away in warm water or by some other suitable method,leaving a photographicimage l firmly embedded in gelatin which ishardened thereby and anchored on to the hydrophilic base.

Washing away is halted at the surface of the hydrophilic material whichimmediately leaves water-receptive portions and slightly upstandinggrease-receptive printing portions. It will be seen that there isefiected a novel step of hardening a silver salt in gelatin and at thesame time the gelatin is firmly anchored to the base of hydrophilicmaterial, with the hydrophilic material cooperating to embed the gelatinintimately therein.

The hydrophilic support/provides a bond for securing the gelatin notpossible with supports such as metal or glass, which greatly increasesthe ability of the gelatin to comprise the printing portions of aplanographic printing plate and withstand press operation.

The exposure can be quickly effected with a simple incandescent lamp inplace of extended exposure to actinic light as is necessarywith chromicsalts. This is important in connection with the speed of preparation andsize of plate which may be obtained. Other procedures for washing ordeveloping unexposed portions of colloid and halide salt away may beresorted to in place of the warm water cited, and similarly variousdeveloping, fixing, and bleaching agents may be resorted to in place ofthe specific ones set forth. It may further be desired to employ atranslucent support for receiving the hydrophilic coating and emulsionas for instance supports of translucent resins or translucent papers.This further increases the utility of the lightsensitive element.

Several other advantages are obtained from the light-sensitive printingelement and process of development set forth. The apparatus for exposureis greatly simplified. The coating of the printing plate support with asilver salt does not have to be effected while the salt is freshlyprepared and as a result web coating operations may be resorted to whichgreatly facilitate and cheapen any such coating operations.

It will be seen that a novel printing member has been provided and ahighly desirable combination efiected of a light-sensitive film with ahydrophilic film. Various savings in time, equipment and handling arethereby effected.

While there has been described a preferred embodiment of the invention,including specific materials and procedures, it should be understoodthat various other materials than those noted may be resorted to inkeeping with the scope of the invention as defined by the appendedclaims.

Having described our invention, we claim:

1. As an article of manufacture a light-sensitive element comprising asupport, said support presenting thereon a film of hydrophilic polyvinylalcohol, a water-soluble colloid layer disposed over said film. saidcolloid having contained therein a silver halide light-senstive salt.

2. A light-sensitive element for use in preparing a planographicprinting plate comprising a base member, a layer of a hydrophilicpolyvinyl alcohol on said base, the hydrophilic polyvinyl alcoholbeing-adapted to receive moisture and comprise non-printing portions ofa planographic printing plate, a coating of a photosensitive emulsion ofgelatin and a silver halide superimposed on the layer of polyvinylalcohol, said layer of polyvinyl alcohol having incorporated thereinsmall amounts of the photosensitive emulsion.

3. A an article of manufacture a light-sensitive element for use inpreparing a planographic printing plate, said light-sensitive elementincluding a base, a layer of a hydrophilic polyvinyl alcohol overlyingsaid base, a photosensitive emulsion of gelatin and a silver halidecoated over said hydrophilic alcohol, the gelatin and silver halidebeing impregnated in the hydro-- philic alcohol, thereby to bond thephotosensitive emulsion to the polyvinyl alcohol.

4. As an article of manufacture a lightsensitive element for use inpreparing a planographic printing plate, said light-sensitive elementincluding a base, a layer of a hydrophilic polyvinyl alcohol overlyingsaid base, a coating of a photosensitive emulsion of gelatin and asilver halide superimposed on the polyvinyl alcohol layer, underlyingportions of the coating of photosensitive emulsion extending into thepolyvinyl alcohol layer.

' WILLIAM CRAIG TOLAND.

ELLIS BASSIST.

